Using STL algorithms, is it better to pass a function pointer or a functor?

Question

Which of these 2 methods is better and why?

Method 1:

void fun(int i) {
  //do stuff
}

...
for_each(a.begin(), a.end(), fun);

Method 2

Answer 1

One big advantage of a function object over a function pointer is that you can more easily bind up some arguments at function object construction.

An example of a functor that might do this would be

  class multiplyBy
  {
  private:
      int m_whatToMultiplyBy;
  public:
      multiplyBy(int whatToMultiplyBy) : 
          m_whatToMultiplyBy(whatToMultiplyBy)
      {
      }

      void operator()(int& i)
      {
          i = m_whatToMultiplyBy * i;
      }
  }


  ...

  // double the array
  for_each(a.begin(), a.end(), multiplyBy(2));

This "binding" of arguments can be done quite nicely with boost::bind and boost::function if boost is available to you.